This invention concerns a method for the manufacture of a slot insulation from a molded laminate for dynamo-electric machines, where the continuous resin-impregnated and/or resin-coated carrier bands, made from woven glass filaments, paper and/or other flat surface-forming materials, possess within one section of the slot insulation a laminated thickening of multiple slot insulation thickness by means of inserted reinforcing plies made from similar flat surface materials, as well as a slot insulation manufactured in accordance with this method.
The known methods are primarily employed for the manufacture of molded laminates which are used in electrical engineering as insulative materials in the form of L- and U-shapes, as well as bands of various dimensions, for example, for the insulation of the rotor windings of turbo-generators. In exceptional cases involving the slot wall insulation of these rotors, there is the need for formed parts with diverse wall thicknesses, such as L-profiles with thickened base leg, U-profiles with a thickened base or band profile with one thickened section. In order to manufacture such slot insulations with partially thickened areas, i.e., with diverse wall thicknesses, it has been necessary heretofore to produce, for example, in case of the above mentioned L-profile with thickened base leg, or a U-profile with thickened base, standard L- or U-shaped profiles and to accomplish the thickening by glueing subsequently specially manufactured small strips to the foot or the base respectively of the standard pieces. It is also possible to use two separately manufactured strip profiles and to glue these parts together in such manner that the desired sections of the slot insulation will be thickened. Usually, these parts will then require finishing operations by grinding and possible a surface treatment by use of varnish.
Slot insulations for rotating electric machines, and especially for high-output machines are primarily used in known manner in the form of fiber-reinforced molded plastic parts, for example, glassfiber-reinforced plastics (GFK). These are laminated and compressed substances with a high mechanical resistance which consist of continuous, laminated resin-carrying bands, using thermosetting resins as bonding agents, for example, the so-called hard-glass fabric, made from woven glass filaments and epoxide resin, materials which possess good electrical and thermal properties. These bands which are laminated in layers and are resin-impregnated and/or resin-coated are compounded under pressure and heat into a uniform and mechanically firm material of a desired thickness and quality.
Not only glass filament fabrics but also "roving" fabrics, glass mats and other insulating flat-surface materials, such as polyamide paper known under the tradename "Nomex," insulating foils, fine mica paper and the like, and combinations thereof can be used for the individual layers of the laminated and compressed substance.
There are other methods known where standard uniform profiles are manufactured by use of molds and pressing. Another method to manufacture profiles of laminated and compressed substances of high electrical strength, dimensional stability and of any desired length is disclosed by the published German application No. 2,113,741 where the forward movement by a pre-set distance of the reinforced band, impregnated or coated with resin, is carried out from the entrance side of the extrusion die to its center in several steps and corresponding pressing operations.
Finally, there are known from the Swiss Pat. Nos. 549,467 and 563,872 laminated and compressed substances for the insulation of electric machines and apparatus, especially for the slot insulation, with an insulative layer of high dielectric strength and resistance to temperature influences and arranged between outer layers of fiber-reinforced carrier material which is laminated for stiffening purposes and is impregnated with thermosetting resin binders, where the inner insulative layer is covered on both sides with tangled fiber layers and where these tangled fiber layers have a core which contains nothing but tangled fibers, being free of any binding agents. These new multi-layer slot insulations possess, in comparison with laminated and compressed substances of pure glass filament fabrics, a substantially improved mechanical strength and will therefore prevent in a more reliable manner electrical punctures during operations.
In order to manufacture a band that is thickened throughout a partial area only, it has been proposed to mold a plate with an overall thickness that is equal to the partial increased thickness, where the profile in the partial area, for example, the center zone, is formed by an appropriate extrusion die. The final profile is then completed by removal of the protruding outer areas, a method which is disadvantageous in view of the relatively large losses of material and the injurious cut of the fabric layers, for example, in case of a glass filament fabric.
If resin-impregated or resin-coated carrier materials are treated with a great amount of resin excess, it becomes possible to fill some hollow spaces with the pure resin that has been forced off but these accumulations of pure resin will have an adverse effect under mechanical stresses because cracks will develop within these areas of pure resin even at slight deformations, cracks which will have the tendency to spread from there, thus creating mechanical and electric trouble spots.